Uasb water treatment process

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2sakil.iubat@gmail.com

Introduction
The total volume of water on Earth is about 1.4 billion km3.
The volume of freshwater resources is around 35 million
km3, Of these freshwater resources, about 24 million km3 or
70 percent is in the form of ice and permanent snow cover in
the Antarctic and Arctic regions.

Domestic households, industrial and agricultural
practices produce wastewater that can cause pollution of
many lakes and rivers.
Industry is a huge source of water pollution, it produces
pollutants that are extremely harmful to people and the
environment.

One of the more interesting new processes is the up flow anaerobic sludge
blanket process (UASB), which was developed by Lettinga and his co-
workers in Holland in the early 1970's
Anaerobic granular sludge bed technology refers to a special kind of
reactor concept for the "high rate" anaerobic treatment of wastewater.

• Sewage is greatest source of aquatic pollution & public health concern in urban areas of
developing countries.
• Domestic sewage is defined as human excreta, urine, and the associated sludge (collectively
known as blackwater), as well as, kitchen wastewater and wastewater generated through
bathing (collectively known as greywater.
Several technology in the field of wastewater treatment:
*Conventional aerobic treatment in ponds
*Trickling Filters ,RBC ,ASP
*Anaerobic treatment
*Combination of Anaerobic And Aerobic Treatment
Adequate treatment system have to be :
•Simple in design
•Efficient in removing the pollutants
•Energy consumption should be low
•Re use of water for use purpose
•Use of sophisticated equipment must be kept to a minimum.

Anaerobic Waste Treatment : An Overview
Historical development:
Mainly used for reducing mass of high solids wastes, e.g. human waste
(night soil), animal manure, agricultural waste and sludge
Early applications of anaerobic waste treatment include:
Mouras automatic scavenger - cited in French journal cosmos in 1881
Septic tank- developed by Donald Cameron in 1895 (England)
Imhoff tank: developed by Karl Imhoff in 1905 (Germany)

Aerobic treatment process - considerable progress in short span of time.
Anaerobic technology: energy crisis in 70 and 80’s- a renewed interest in
anaerobic process
0
200
400
600
800
1000
1200
1978
1981
1984
1987
1990
1993
1996
1999
No.ofplants
Anaeroic treatment plants for industrial applications (Source: Frankin, 2001)

Definition:
Anaerobic treatment is a biological process carried out in the absence
of O2 for the stabilization of organic materials by conversion to CH4
and inorganic end-products such as CO2 and NH3.
Organic materials + Nutrients CH4 + CO2 +NH3 + Biomass
Anaerobic microorganisms
Anaerobic processes
Anaerobic fermentation Anaerobic respiration
Anaerobic Waste Treatment

COMPLEX ORGANIC MATTERS
Proteins Carbohydrates Lipids
Amino Acids, Sugars Fatty Acids, Alcohols
hydrolysis
Acetate Hydrogen, Carbon dioxide
acetogenesis
INTERMEDIARY PRODUCTS
(C>2; Propionate, Butyrate etc)
acidogenesis
Methane
Carbon dioxide
Overview Anaerobic Biodegradation
methanogenesis

Doubling Time Cell Yield Cell Activity ks
days g VSS g-1 COD g COD g-1 VSS d-1 mM
Active Sludge (sugar)
Aerobic Bacteria 0.030 0.40 57.8 0.25
Acidification (sugar)
Fermentative Bacteria 0.125 0.14 39.6 ND
Acetogenesis (fatty acids)
Acetogenic Bacteria 3.5 0.03 6.6 0.4
Methanogenesis
Autotrophic (H2) 0.5 0.07 19.6 0.004
Acetoclastic (acetate)
Methanosarcina 1.5 0.04 11.6 5.0
Methanosaete 7.0 0.02 5.0 0.3
Kinetic Parameters Anaerobes

Methanosaeta Methanosarcina
Growth kinetics of Methanosarcina and Methanosaeta

COD Balance
Aerobic
Biodegradation
COD Balance
Anaerobic
Biodegradation

Essential conditions for efficient anaerobic treatment
• Enough nutrients (N & P) and trace metals especially, Fe, Co, Ni, etc.
COD:N:P = 350:7:1 (for highly loaded system) 1000:7:1 (lightly
loaded system)
• Avoid excessive air/O2 exposure
• No toxic/inhibitory compounds present in the influent
• Maintain pH between 6.8 –7.2
• Sufficient alkalinity present
• Temperature around mesophilic range (30-38 oC)

Environmental factors
The successful operation of anaerobic reactor depends on maintaining the
environmental factors close to the comfort of the microorganisms
involved in the process.
Rule of thumb: Rate of a reaction doubles for every 10 degree
rise in temperature
Psychrophilic (5 - 15oC)
Mesophilic (35 – 40 C)
Thermophilic (50-55 oC)
Temperature

Relative activity of methanogens to pH
0.0
0.3
0.5
0.8
1.0
1.3
3 4 5 6 7 8 9 10 11
pH
Activity
pH range for acidogens is 5.5 – 6.5
Methanogensis 7.8 – 8.2.
operating pH for combined cultures is 6.8-
7.4 with neutral pH being the optimum
pH
Since methanogenesis is
considered as a rate limiting
step, It is necessary to
maintain the reactor pH close
to neutral.

All microbial processes including anaerobic process requires macro (N, P
and S) and micro (trace metals) nutrients in sufficient concentration to
support biomass synthesis. In addition to N and P, anaerobic
microorganisms especially methanogens have specific requirements of trace
metals such as Ni, Co, Fe, Mo, Se etc. The nutrients and trace metals
requirements for anaerobic process are much lower as only 4 - 10% of the
COD removed is converted biomass.
Nutrients and trace metals
COD:N:P = 350:7:1
Inhibition/Toxicity
The toxicity is caused by the substance present in the influent waste
or byproducts of the metabolic activities. Ammonia, heavy
metals, halogenated compounds, cyanide etc. are the examples of
the former type whereas ammonia, sulfide, VFAs belong to latter
group.

Anaerobic Aerobic
Organic loading rate:
High loading rates:10-40 kg COD/m3-day Low loading rates:0.5-1.5 kg COD/m3-day
(for high rate reactors, e.g. AF,UASB, E/FBR) (for activated sludge process)
Biomass yield:
Low biomass yield:0.05-0.15 kg VSS/kg COD High biomass yield:0.37-0.46 kg VSS/kg COD
(biomass yield is not constant but depends
on types of substrates metabolized)
(biomass yield is fairly constant irrespective
of types of substrates metabolized)
Specific substrate utilization rate:
High rate: 0.75-1.5 kg COD/kg VSS-day Low rate: 0.15-0.75 kg COD/kg VSS-day
Start-up time:
Long start-up: 1-2 months for mesophilic
: 2-3 months for thermophilic
Short start-up: 1-2 weeks
Comparison between anaerobic and aerobic processes

Anaerobic Aerobic
SRT:
Longer SRT is essential to retain the slow
growing methanogens within the reactor.
Microbiology:
Anaerobic process is multi-step process
and diverse group of microorganisms
degrade the organic matter in a
sequential order.
Aerobic process is mainly a one-species
phenomenon.
Environmental factors:
The process is highly susceptible to
changes in environmental conditions.
SRT of 4-10 days is enough in case of
activated sludge process.
The process is less susceptible to
changes in environmental conditions.
Continue..….

Advantage of anaerobic process
1. Less energy requirement as no aeration is needed
0.5-0.75 kwh energy is needed for every 1 kg of COD removal by aerobic process
2. Energy generation in the form of methane gas
1.16 kwh energy is produced for every 1 kg of COD removal by anaerobic process
3. Less biomass (sludge) generation
Anaerobic process produces only 20% of sludge that of aerobic process
Soluble BOD
1 kg
Aerobic process
CO2 + H2O
0.5 kg
New biomass
0.5 kg
Biodegradable
COD
1 kg
Anaerobic process
CH4 gas
> 0.9 kg
New biomass
< 0.1 kg

4. Less nutrients (N & P) requirement
Lower biomass synthesis rate also implies less nutrients requirement : 20%
of aerobic
5. Application of higher organic loading rate
Organic loading rates of 5-10 times higher than that of aerobic processes are
possible
6. Space saving
Application of higher loading rate requires smaller reactor volume thereby saving
the land requirement
7. Ability to transform several hazardous solvents including
chloroform, trichloroethylene and trichloroethane to an
easily degradable form

1. Long start-up time
Because of lower biomass synthesis rate, it requires longer start-up time to
attain a biomass concentration.
2. Long recovery time
If an anaerobic system subjected to disturbances either due to biomass wash-out,
toxic substances or shock loading, it may take longer time for the system to return
to normal operating condition.
3. Specific nutrients/trace metal requirements
Anaerobic microorganisms especially methanogens have specific nutrients
e.g. Fe, Ni, and Co requirement for optimum growth.
4. More susceptible to changes in environmental conditions
Anaerobic microorganisms especially methanogens are prone to changes in
conditions such as temperature, pH, etc.
Limitations of anaerobic processes

5. Treatment of sulfate rich wastewater
The presence of sulfate not only reduces the methane yield due to substrate
competition but also inhibits the methanogens due to sulfide production.
6. Effluent quality of treated wastewater
The minimum substrate concentration (Smin) from which microorganisms are able to
generate energy for their growth and maintenance is much higher for anaerobic
treatment system. Owing to this fact, anaerobic processes may not able to degrade
the organic matter to the level meeting the discharge limits for ultimate disposal.
7. Treatment of high protein & nitrogen containing wastewater
The anaerobic degradation of proteins produces amines which are no longer be
degraded anaerobically. Similarly nitrogen remains unchanged during anaerobic
treatment. Recently, a process called ANAMMOX ( ANaerobic AMMonium OXididation)
has been developed to anaerobically oxidize NH4
+ to N2 in presence of nitrite.
NH4
+ + NO2
- N2 + 2H2O

Types of anaerobic reactors
Low rate anaerobic reactors High rate anaerobic reactors
Anaerobic pond
Septic tank
Standard rate
anaerobic digester
Imhoff tank
Anaerobic Sequencing Batch
Reactor (ASBR)
Anaerobic contact process
Anaerobic filter (AF)
Upflow anaerobic slugde
Blanket (UASB)
Fluidized bed Reactor
Hybrid reactor: UASB/AF
Slurry type
bioreactor, temperature, mixing, SRT or
other environmental
conditions are not regulated. Loading
of 1-2 kg COD/m3-day.
Able to retain very high concentration of
active biomass in the reactor. Thus
extremely high SRT could be maintained
irrespective of HRT. Load 5-20 kg COD/m3-d
COD removal efficiency : 80-90%
.

UASB was developed in 1970s by Lettinga in the Netherlands.
UASB is essentially a suspended growth system in which proper hydraulic and organic loading rate is
maintained in order to facilitate the dense biomass aggregation known as granulation. The size of
granules is about 1-3 mm diameter. Since granules are bigger in size and heavier, they will settle
down and retain within the reactor. The concentration of biomass in the reactor may become as
high as 50 g/L. Thus a very high SRT can be achieved even at very low HRT of 4 hours.
The granules consist of hydrolytic
bacteria, acidogen/acetogens
and methanogens. Carbohydrate
degrading granules show
layered structure with a surface layer of
hydrolytic/fermentative
Acidogens. A mid-layer comprising of
syntrophic colonies and an interior with
acetogenic methanogens.
Upflow Anaerobic Sludge Blanket
(UASB)

gas
cap
3 phase
separator
weir
settler
baffles
influent
effluent
gas bubble
sludge granule
biogas
Upward-flow Anaerobic Sludge Blanket
sludge
bed

Anaerobic Sludge Granules
Physical: dense compact biofilms
high settleability
high mechanical strength
Microbial: balanced microbial community
syntrophic partners closely associated
high methanogenic activity
(0.5 to 2.0 g COD/g VSS.d)
protection from toxic shock

The spaghetti theory of granulation
I) disperse methanogens (filamentous Methanosaeta
II) floccule formation via entanglement
III) pellet formation ("spaghetti balls");
IV) mature granules,
with attachment of other anaerobic microorganisms onto the pellet.
proposed by Dr. W. Wiegant

Anaerobic Sludge Granules (close up)

Acetate as Substrate
(Methanosaeta)
Sucrose as Substrate (mixed
culture)
Anaerobic Sludge Granules (SEM)
dispersed
Anaerobic Sludge Granules (settling)
flocculentgranular

Influent
Effluent
Recycle
Sludge
Bed
Effluent settler
gas
cap
biogas
gas
bubble
sludge
granule
Expanded
Granular Sludge
Bed
An expanded granular sludge bed (EGSB)
reactor is a variant of the UASB concept (Kato et
al. 1994). The distinguishing feature is that a
faster rate of upward-flow velocity is designed for
the wastewater passing through the sludge bed.
The increased flux permits partial expansion
(fluidization) of the granular sludge
bed, improving wastewater-sludge contact as
well as enhancing segregation of small inactive
suspended particle from the sludge bed. The
increased flow velocity is either accomplished by
utilizing tall reactors, or by incorporating an
effluent recycle

Anaerobic contact process (ACP)
Anaerobic contact process is essentially an anaerobic activated
sludge process. It consists of a completely mixed reactor followed
by a settling tank. The settled biomass is recycled back to the
reactor. Hence ACP is able to maintain high concentration of
biomass in the reactor and thus high SRT irrespective of HRT.
Degassifier allows the removal of biogas bubbles (CO2, CH4)
attached to sludge which may otherwise float to the surface..
Influent Effluent
Waste sludge
Recycled sludge
Completely mixed
reactor
Biogas
Degassifier
Biogas
Settling tank

Anaerobic filter
• Anaerobic filter: Young and McCarty in the late 1960s
for treat dilute soluble organic wastes.
• The filter was filled with rocks similar to the trickling filter.
• Wastewater distributed across the bottom and the flow was in
the upward direction through the bed of rocks
• Whole filter submerged completely
. Anaerobic microorganisms accumulate within voids of media
(rocks or other plastic media)
• The media retain or hold the active biomass within the filter
• The non-attached biomass within the interstices forms a bigger
flocs of granular shape due to rising gas bubble/liquid
• Non-attached biomass contributes significantly to waste treatment
• Attached biomass not be a major portion of total biomass.
• 64% attached and 36% non-attached

Upflow Anaerobic Filter
Feeding
Tank at 4oC
Bio gas
Effluent
Peristaltic Pump
Media
Perforated
Aluminum Plate Sampling
Port
Heater
Constant Temperature
Recirculation Line
Water Bath
Peristaltic Pump
Sludge Wastage

Originally, rocks were employed as packing medium in
anaerobic filter. But due to very low void volume (40-50%),
serious clogging problem was witnessed. Now, many
synthetic packing media made up of plastics, ceramic tiles
of different configuration have been used in anaerobic filters.
The void volume in these media ranges from 85-95 %.
Moreover, these media provide high specific surface area
typically 100 m2/m3 or above which enhance biofilm growth.
Since anaerobic filter is able to retain high biomass, long SRT
could be maintained. Typically HRT varies from 0.5 – 4 days and
the loading rates varies from 5 - 15 kg COD/m3-day. Biomass
wastage is generally not needed and hydrodynamic conditions
play important role in biomass retention within the void space 36sakil.iubat@gmail.com

Multi-fed Up Flow Anaerobic Filter (MUAF)
Waste is fed through several points along the depth of filter.
Such feeding strategy has unique benefits::
Wastewater
Inletpoints
Effluent
1. Homogeneity in biomass distribution
2. Maintenance of completely mixed
regime thus preventing short -
circuiting and accumulation of VFA.
3. Uniform substrate concentration within
the reactor and prevent heavy biomass
growth at bottom thus avoids clogging
4. Effective utilization of whole filter bed

UASB
EGSB
Hybrid
Anaer Filt
Fluid. Bed
Contact
Undefined
UASBEGSB
contact
?
hybrid
anaer. filt.
fluid. bed
EGSB+UASB = 72%
Market-Share Granular Sludge Reactors

OPTIONS FOR POST-TREATMENT OF
ANAEROBIC REACTOR EFFLUENTS
Beginning with a typical municipal raw wastewater, this level of treatment will generally result
in an “enhanced primary” effluent quality, intermediate between primary and secondary
(between 30-70 mg/l for BOD5). Post-treatment should be designed to improve the effluent
quality in the following parameters.
*pathogen contamination (measured by the index of E. coli);
*residual organic material (COD/BOD5);
*oxygen demand from the reduced forms of N and S;
*residual suspended solids (TSS)
*inorganic N and P (nutrients)
Pond systems
Constructed wetlands
duckweed
Mechanical aerated post treatment
basic types of post treatment processes are:

The government of India has made a major commitment to anaerobic
treatment technology in its national river basin improvement program. As
of 1996, thirteen new anaerobic treatment plants, with an aggregate
treatment capacity of over 306 MLD are under construction in India. The
treatment plants described below have been in operation long enough to
be able to evaluate their treatment effectiveness and their financial and
economic costs and benefits:
Indian Scenario
A 5 MLD plant in Kanpur, in the state of Uttar Pradesh, built in the
late 1989,
A 14 MLD plant in Mirzapur, Uttar
Pradesh, based on the Kanpur pilot plant
design, was commissioned in 1991,
A 36 MLD plant in Kanpur reached full performance in
1994, treating a mixture of up to 75 percent municipal
wastewater and 25 percent tannery effluent.

The UASB-process represents one important option for sewage
purification in countries with warm climates as it meets the above
mentioned basic necessities for a sustainable operation of wastewater
treatment plants in developing countries like
• Low investment costs,
• Low maintenance demand,
• Good performance,
• Low sludge production
• Net energy production.
Concluding remarks

References
Journal papers
Machdar, Y.Sekiguchi,H.Sumino,A.Ohashi,and H.Harada(1997).combination of a UASB reactor and a curtain type DHS
reactor as a cost-effective sewage treatment system for developing countries.Wat.Sci.Tech vol 42 Nos 3-4 pp83-88 IWA
publishing 2000.
R.A.Barbosa and G.L.Sant’Anna Jr(1989).Treatment Of Domestic Sewage In An UASB Reactor.Wat . Res. Vol.23 , No. 12 pp
1483-1490,1989.
G.Lettinga, R.Roersma, and P.Grin, (1983)Anaerobic Treatment of Raw Domestic Sewage At Ambient Temperature Using
Agranular Bed UASB reactor.Biotechnology and Bioengineering , vol XXV,pp1701-1723,1983.
S.M.M.Vieira and A.D. Garcia Jr.(1992) Sewage Treatment By UASB Reactor ,operation results and recommendation for
design and utilization ,Wat.Sci..Tech. Vol.25 No.7 pp.143-157,1992.
Sonia M.M. Vieira (1988)Anaerobic Treatment of Domestic Sewage in Brazil – Reaserch Results And Full – scale Experience
,Anaerobic Digestion vol.14 1988.
Lalit k . Agarwal , * Hideki Harda and Hiroyuki Okui (1997) Treatment of dilute wastewater in a UASB reactor at a Moderate
Temperature : Performance Aspects,Journal of Fermentation and Bioengineering vol.83 ,No. 2 , 179-184.1997.
Lalit k . Agarwal , * Hideki Harda and Hiroyuki Okui, Cheng Tseng (1997) Treatment of Wastewater in a UASB Reactor at a
Moderate temperature : Microbiological aspects.,Journal of Fermentation and Bioengneering Vol83, No,2 185-190 .1997
Hideki Harda , Shigeki Uemura and Kiyoshi Momonoi(1994) Interaction between sulphate reducing bacteria and methane
producing bacteria in UASB reactors fed with low strength wastes containing different levels of sulphate, Wat. Res. Vol.28
No.2 pp 355-367,1994.
A.Schellinkhout * and J.Collazos** (1992) Full – Scale Application of the UASB technology For Sewage Treatment, Wat. Res.
Vol. 25 No. 7 .PP 159-166.1992
.
A.R.M van der Last and G. Lettinga (1992) Anaerobic Treatment of domestic sewage under moderate climatic (dutch)
conditions using upflow reactor at increased superficial velocities ,Wat.Sci .Tech. Vol 25 No. 7 pp 167-178 .1992

Lucas Seghezzo, Grietje Zeeman * Jules B .Van Lier , H.V.M Hamlelers & Gatze Lettinga (1998) , A Riview :
The Anaerobic Treatment Of Sewage in UASB And EGSB Reactors, Biresource Technology 65 (1998) 175-190 .
Juan Carlos Parajo , Herminia Dominguez & Jose Manuel Dominguez , Biotechnological products of Xylitol
. Part 1: Interest of Xylithol and fundamentals of its biosynthesis , Bioresource technology 65 (1998) 191-
201.
H. Draaijier , J.A.W.Maas ** , J.E.Schaapman ** and A. Khan (1992) Performance of the 5 MLD UASB
reactor for sewage treatment at Kanpur ,India. Wat.Sci>Tech.Vol.25 No.7 pp123-133,1992.
S.M.M.Viera ,J.L.Carvalho, F.P.O Barijan (1994),Application of the UASB technology for Sewage Treatment in
small Community at Sumare, Sao Paulo state, Wat.Sci. Vol.30,No.12.pp 203- 210 .1994 .
J.H.F.Pereboom (1994) ,Size Distribution Model For Methanogenic Granules From Full Scale UASB and IC
reactors, Wat Sci. Tech. Vol.30 , No. 12 pp 211-221, 1994.
J.J.Bogte ,A.M.Breure, J.G.van Andel and G.Lettinga(1993) Anaerobic Treatment of domestic Wastewater in
small scale UASB reactors ,Wat.Sci. Vol.27 No.9 pp 75-82 ,1993.
Lalit K Agarwal , Yasuhiro Ohashi , Etsuo Mochida , Hiroyuki Okui , Yasuko Ueki , Hideki Harda and Akiyoshi
Ohashi(1997),Treatment of Raw Sewage In a temperate climate using a UASB reactor and the Hanging
Sponge Cubes Process, Wat. Sci. Tech. Vol.36 No. 6-7 pp 433-440, 1997 .
S.K.I.Sayed and M.A.A Fergala(1995) Two – stage UASB concept treatment of domestic sewage including
sludge stabilization process, Wat. Sci. Tech. Vol. 32 .No.11 pp 55-63, 1995
Lucas seghazzo (2004) Anaerobic treatment of domestic wastewater in subtropical region .,thesis
wageningen university , the Netherlands with references with summaries in English , Dutch and
Spanish.,2004
Cavalcanti, Paula Frassinetti Feitosa(2003) , Integrated application of the UASB reactor and ponds for
domestic sewage treatment in tropical regions. Thesis Wageningen University, Wageningen, The Netherlands
- with references – with summary in English, Dutch and Portuguese. xiv + 141 p.

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